Method for deicing and cleaning of fans

ABSTRACT

The invention pertains to a method for removing ice layers and/or snow layers and/or dirt layers from the rotor blades (B) of axial fans in cooling installations for refrigerating and/or freezing products. At least one cleaning substance jet (S) is directed toward the rotor blades (B) of an axial fan within certain time intervals in such a way that ice layers and/or snow layers and/or dirt layers are at least separated from the surfaces of the rotor blades (B) and transported away, wherein the rotor blades (B) rotate with nominal speed while cleaning jets (S) act upon their surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.12/297,720, which was the National Stage of International ApplicationNo. PCT/EP2007/001427, filed Feb. 19, 2007, and such applications arehereby incorporated by reference in entirety.

BACKGROUND OF THE INVENTION

The invention pertains to a method for removing ice layers and/or snowlayers and/or dirt layers from the rotor blades of axial fans in coolinginstallations for refrigerating and/or freezing products, as well as toan apparatus for carrying out this method.

An axial fan as it is sufficiently known from the state of the art is afluid flow engine that is equipped with a rotor, on the circumference ofwhich rotor blades are arranged. Due to the geometry of the rotorblades, the rotating rotor is able to take in gas and pass on the gas inthe direction of its rotational axis (axially) with increased pressure,wherein this is the reason why rotor blades have so-called suction sidesand pressure sides.

In order to refrigerate and/or freeze products, particularly foodproducts, is common practice to utilize refrigerating devices, in whichthe products are transported through a treatment zone, wherein heat ofthe products is absorbed in said treatment zone by a cool atmosphere.One popular refrigerating device, for example, is a so-called tunnelfroster, in which food products are brought in contact with cold gassuch as, e.g., cold carbon dioxide, nitrogen or cold air and thuslyrefrigerated and/or frozen while they continuously move through ahousing of tunnel-like design. In order to improve the heat transferfrom the products to the cold atmosphere, the cold atmosphere isfrequently circulated within the treatment zone with the aid of one ormore fans. Part of the humidity that is admitted into the treatment zonewith the products to be refrigerated or the ambient air is absorbed bythe cold atmosphere and precipitated in the form of ice or snow at adifferent location within the refrigerating device. This effect causesthe formation of ice layers or snow layers on solid surfaces,particularly also on the rotor blades of the fans. The geometries of therotor blades in the non-icy state are optimized with respect to theoutput of a fan, i.e., the maximum volumetric flow rate of the coldatmosphere to be circulated by the fan. This means that deviations fromthe optimal geometry as they may be caused by an ice layer reduce theoutput and therefore lower the speed of the cold gas flowing past theproducts. The same effect also occurs when dirt layers are deposited onrotor blades.

The heat transfer between a solid body and a gas is highly dependent onthe relative speed between the gas and the solid body: the lower therelative speed, the worse the heat transfer. Consequently, ice layersand/or dirt layers on the rotor blades of fans lead to a deteriorationof the heat transfer from the products to be refrigerated to the coldatmosphere and therefore to a reduced refrigerating capacity of arefrigerating device. If the refrigerating capacity falls short of apredetermined value, it is necessary to interrupt the production ofapparatuses according to the state of the art in order to open therefrigerating device and to clean the rotor blades. Ice layers and/ordirt layers deposited on rotor blades therefore significantly affect theefficiency of such refrigerating and/freezing methods.

SUMMARY OF THE INVENTION

The present invention consequently is based on the objective ofdisclosing a method of the initially described type that makes itpossible to quickly remove ice layers and/or snow layers and/or dirtlayers on rotor blades without having to interrupt the production.

According to the invention, this objective is attained in that at leastone cleaning substance jet is directed toward the rotor blades of anaxial fan within certain time intervals in such a way that ice layersand/or snow layers and/or dirt layers are at least separated from thesurfaces of the rotor blades and transported away, wherein the rotorblades rotate with nominal speed while cleaning jets act upon theirsurfaces.

Ice layers and/or snow layers and/or dirt layers on rotor blades areremoved during the continued production with such a method. However, theoutput of the fan is reduced during a cleaning method carried out inaccordance with the invention due to the altered flow conditions. Sincesuch an inventive cleaning process is completed within less than twoseconds, however, it only affects the refrigerating capacity of therefrigerating device insignificantly. It is therefore sensible to repeatthe inventive cleaning process within shorter time intervals than acleaning process according to the state of the art.

The cleaning jets are preferably produced with cleaning nozzles. If thecleaning jet consists of a gas jet, the cleaning jets are advantageouslygenerated by means of supersonic nozzles such that the cleaning jetshave a supersonic speed—at least at the outlet of the cleaning nozzles.Due to the utilization of supersonic nozzles, gaseous cleaning jets withhigh momentum and therefore high cleaning effect are produced.

According to the invention, the cleaning jets consist of substances thatdo not lead to a contamination of the products being refrigerated and/orfrozen in the refrigerating device and do not freeze to any location ofthe refrigerating device. The cleaning jets therefore preferably consistof dehumidified compressed air or nitrogen or carbon dioxide gas ormixtures of nitrogen and/or carbon dioxide gas and/or dehumidifiedcompressed air.

According to one variation of the inventive method, cleaning jets thatcontain solid carbon dioxide (dry ice) are produced of liquid,pressurized carbon dioxide by means of suitable expansion. Thisvariation is particularly suitable for cleaning rotor blades inrefrigerating devices, in which liquid carbon dioxide is used forrefrigerating and/or freezing products.

According to another variation of the inventive method, a mixture of asuitable gas and a granulate consisting of solid carbon dioxide (dryice) is used for producing the cleaning jets.

According to the invention, the gas for producing cleaning jets is fedto the cleaning nozzles with a pressure that lies between 1 and 60 bar,preferably between 1 and 20 bar.

According to one variation of the inventive method, at least onecleaning nozzle is arranged in the plane of rotation of the rotor bladesto be cleaned and spaced apart from the rotor blades such that thecleaning jet produced by the cleaning nozzle extends in the plane ofrotation of the rotor blades to be cleaned. If a cleaning nozzle isarranged in this fashion, the cleaning jet acts upon the suction sideand the pressure side of the rotor blades and removes ice layers and/orsnow layers and/or third layers adhering thereto.

According to another variation of the inventive method, cleaning nozzlesare arranged on the suction side and on the pressure side of the rotorblades to be cleaned in such a way that the cleaning jets produced bythe cleaning nozzles act upon the surfaces of the rotor blades to becleaned.

According to the invention, each cleaning nozzle is arranged in such away that the smallest distance between the cleaning nozzle and a rotorblade lies between 1 and 100 mm, preferably between 1 and 20 mm.

According to an additional development of the inventive method, it isproposed that the rotor blades are cleaned in a time-controlled fashion,wherein the time interval between two successive cleaning processespreferably lies between 1 and 60 min. According to one variation of theinventive method, a cleaning process is triggered as soon as therefrigerating capacity of the refrigerating device falls short of acertain value or as soon as the power required for driving the rotorblades to be cleaned exceeds or falls short of a certain value.

The invention furthermore pertains to an apparatus for removing icelayers and/or snow layers and/or dirt layers from the rotor blades ofaxial fans in cooling installations for refrigerating and/or freezingproducts.

With respect to the apparatus, the aforementioned objective is attainedin that at least one device for producing a cleaning substance jet isarranged in the vicinity of the rotor blades and able to produce acleaning substance jet that is directed toward the rotor blades withincertain time intervals, wherein this cleaning substance jet separatesand transports away ice layers and/or snow layers and/or dirt layers onthe surfaces of the rotor blades due to its momentum.

According to one preferred embodiment of the inventive apparatus, thedevice for producing a cleaning substance jet consists of a nozzle(cleaning nozzle) that can be supplied with a substance or a substancemixture in order to produce the cleaning jet.

According to an additional development of the inventive apparatus, it isproposed that one or more cleaning nozzles are arranged in the plane ofrotation of the rotor blades to be cleaned and aligned such that thecleaning jets produced by the cleaning nozzles extend in the plane ofrotation of the rotor blades and are directed toward the rotational axisof the rotor blades.

According to one embodiment of the inventive apparatus, at least onecleaning nozzle is arranged on the suction side and at least one othercleaning nozzle is arranged on the pressure side of the rotor blades tobe cleaned, wherein each of the cleaning nozzles is aligned such thatthe cleaning jet produced by the cleaning nozzle is directed toward thesurfaces of the rotating rotor blades.

According to another preferred embodiment of the inventive apparatus,the cleaning nozzles are realized in the form of supersonic nozzlessuitable for producing gaseous cleaning jets that exit with supersonicspeed.

Each of the cleaning nozzles is advantageously arranged at a minimumdistance from the rotor blades that lies between 1 and 100 mm,preferably between 1 and 20 mm.

The invention is suitable for cleaning rotors of axial fans in allconceivable cooling installations for refrigerating and/or freezingproducts. The advantages attained with the invention manifestthemselves, in particular, in devices with treatment zones, into whichlarge quantities of humidity are admitted, for example, in tunnelfrosters for refrigerating and/or freezing food products, particularlyunpackaged food products. Humidity is admitted into the treatment zonesof such tunnel frosters with the food products that generally have ahigh water content, as well as the humid ambient air taken in on bothopen ends of the tunnel froster.

The invention provides a number of advantages compared to the state ofthe art:

The rotor blades of axial fans in refrigerating devices are cleanedwithin shorter time intervals because the cleaning takes place duringthe operation of the refrigerating device, i.e., without interruptingthe production. Consequently, a cleaning process is already carried outat a slightly decreased production capacity such that the averageproduction capacity of an installation for refrigerating and/or freezingis significantly increased. In addition, the effectiveness of a morecomplex production process, in which the refrigerating and/or freezingof products only represents a partial aspect, is also improved due tothe largely constant production capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail below with reference toembodiments that are schematically illustrated in the figures:

In these figures,

FIG. 1 shows a side view and a top view of the rotor of an axial fanwith a nozzle for generating a cleaning jet;

FIG. 2 shows a side view and a top view of the rotor of an axial fanwith four nozzles for generating cleaning jets;

FIG. 3 shows the rotor of an axial fan with two respective nozzle lipsfor generating a multitude of cleaning jets on the suction side and thepressure side, and

FIG. 4 shows the rotor of an axial fan with a hollow drive shaft, fromwhich cleaning jets are ejected through bores.

DETAILED DESCRIPTION OF THE INVENTION

In the four embodiments shown, identical components are identified bythe same reference symbols.

FIG. 1 shows a rotating rotor R of an axial fan that consists of a rotorshaft W that is arranged on the suction side and four rotor blades B.

A nozzle D for producing a cleaning jet S is supplied with nitrogen viaa line 1 and arranged in the plane of rotation of the rotor blades B, aswell as spaced apart from the ends thereof by approximately 10 mm. Thenozzle D is aligned such that the cleaning jet S produced therein isdirected toward the rotor shaft W and extends in the plane of rotationof the rotor blades B. One part SU of the cleaning jet S acts upon thepressure sides of the rotor blades B while the other part SO acts upontheir suction sides. The rotation of the rotor R results in the cleaningjet S acting upon all four rotor blades B and removing ice and dirt fromall sides thereof due to its momentum.

The embodiment illustrated in FIG. 2 differs from the embodimentaccording to FIG. 1 in the number of cleaning jets. Four nozzles Darranged on the circumference of the rotor produce four cleaning jets S.This arrangement results in shorter cleaning times and also has asuperior cleaning performance.

FIG. 3 also shows a rotating rotor R of an axial fan that consists of arotor shaft W arranged on the suction side and four rotor blades B.Nozzle lips DL that respectively feature an open and a closed end arearranged on the suction and the pressure sides of the rotor blades.Gaseous nitrogen is introduced into the nozzle lips DL at the open endsand exits through a multitude of bores D. The bores D act as nozzles andproduce a multitude of cleaning jets S that are directed parallel to therotor shaft W and clean the rotor blades B from both sides.

FIG. 4 shows a rotating rotor R of an axial fan that consists of a rotorshaft W in the form of a hollow shaft arranged on the suction side andfour rotor blades B. The rotor shaft W has an open end and a closed end.Gaseous nitrogen is introduced into the rotor shaft W at the open endand exits through eight bores D. The eight bores D act as nozzles andproduce eight cleaning jets S, wherein one respective cleaning jet S isdirected toward each side of the four rotor blades.

What is claimed is:
 1. A method for removing ice layers and/or snowlayers and/or dirt layers from the rotor blades of axial fans in coolinginstallations for refrigerating and/or freezing products, comprisingdirecting at least one cleaning jet toward the rotor blades of an axialfan within certain time intervals such that ice layers and/or snowlayers and/or dirt layers are at least separated from surfaces of therotor blades and transported away, wherein the rotor blades rotate withnominal speed while the at least one cleaning jet acts upon thesurfaces.
 2. The method according to claim 1, wherein the at least onecleaning jet is produced by means of cleaning nozzles.
 3. The methodaccording to claim 1, wherein the at least one cleaning jet is producedof substances that do not lead to a contamination of the products beingrefrigerated and/or frozen in the cooling installation and do not freezeto any location of the cooling installation.
 4. The method according toclaim 1, wherein the at least one cleaning jet comprises gas selectedfrom dehumidified compressed air, nitrogen, carbon dioxide; and mixturesof nitrogen and carbon dioxide, mixtures of nitrogen and dehumidifiedcompressed air, mixtures of carbon dioxide and dehumidified compressedair, and mixtures of nitrogen, carbon dioxide and dehumidified compressair.
 5. The method according to claim 1, wherein the at least onecleaning comprises solid carbon dioxide (dry ice) produced of liquid,pressurized carbon dioxide by means of suitable expansion.
 6. The methodaccording to claim 1, wherein a mixture of a suitable gas and agranulate comprising solid carbon dioxide (dry ice) is used forproducing the at least one cleaning jet.
 7. The method according toclaim 3, wherein the at least one cleaning jet is produced by means ofat least one supersonic nozzles.
 8. The method according to claims 1,wherein the rotor blades are cleaned in a time-controlled fashion, andwherein a time interval between two successive cleaning processes isfrom between 1 min and 60 min.
 9. The method according to claims 1,wherein cleaning the rotor blades begins when refrigerating capacity ofthe cooling installation falls below a certain value or as soon as powerrequired for driving the rotor blades to be cleaned exceeds or fallsbelow a certain value.